AE04B-A0279 Rev -- FUNCTIONAL DESCRIPTION
Document use is restricted to that described on cover
3-1
CHAPTER 3
FUNCTIONAL DESCRIPTION
3.1 OVERVIEW
The SelectAmp CDMA 800 bi-directional channelized amplifier provides selective frequency amplification of
user specified frequencies in the SMR, Cellular, and ESMR bands. This unit will selectively filter for one 1.25
MHz or 5 MHz channel, depending on the part number ordered, in the Uplink and Downlink band as
determined by the operator. This is accomplished by downconverting the desired signals to a 70 MHz IF
and using narrowband SAW filters to provide adjacent channel rejection.
3.2 FUNCTIONAL DESCRIPTION
Refer to Figure 3-1. Each path in the SelectAmp consists of four major modules: diplexers, LNA/attenuator,
channelizer, and power amplifier. These four modules are powered by, interconnected by, and monitored by
the power supply, interconnect board, and the status and control module respectively. Diplexing of the
uplink and downlink signals is accomplished by diplexer filters tuned to the required band (SMR, Cellular, or
ESMR). This view shows a third LNA/Attenuator for the diversity option.
These modules perform the function of selecting one 1.25 or 5 MHz channel out of the SMR, Cellular, or
ESMR band for amplification.
3.2.1 Diplexer
The diplexer module consists of dual filters with a common port on one end and two separate ports on the
other. One side of the diplexer is tuned for the uplink band, the other side for the downlink band. Insertion
loss of each filter is 2 dB maximum and 65 dB minimum rejection to the opposite band.
3.2.2 LNA/Attenuator
The LNA/attenuator module contains gain stages and digitally controlled attenuators. The gain of this
module is adjustable to permit the overall gain of the downlink path to be adjusted between 65 and 95 dB,
and the uplink path to be adjusted between 55 and 85 dB.
3.2.3 Channelizer
The channelizer module contains three boards shielded by aluminum dividers. These three boards, which
are described below, provide the channel selectivity for the SelectAmp. Overall gain of the Channelizer
module is 5 dB.
3.2.3.1 Downconverter
The downconverter board consists of a mixer driven by a synthesizer, and gain stages. The DC current draw
of each gain stage is monitored by a window comparator for status. The window comparator will indicate a
fault, if the gain stage has an open or short failure. The output of the down converter is fed to the
upconverter board.
